Grinding mill



W. KQHLER Sept. 20, 1938.

GRINDING MILL Filed April 5, 1954 Patented Sept. 20, 1938 i GRINDING MILL Willy Kohler, Neckarhausen/Ladenburg-on-the- Ne'ckar, Germany, assignor to Joseph Voegle V A. G., Mannheim, Germany Application April 5, 1934, Serial No. 719,177 In Germany April 10, 1933 2 Claims. (01. 83-12) This invention relates to improvements in wet ranged to accommodate the material under treatgrinding mills in which the material to be ground ment in the various stages of the series of grindpasses between several smooth surfaced rolls in ing operations, which are shown as carried out the form of a paste or thick fluid. After each by three grinding rolls b, c and g with smooth cy- 5 grinding stage the material under treatment is lindrical surfaces. The rolls are in any usual 5 freed or liberated into a collecting space from manner held in contact under pressure and rowhich it passes to the next grinding stage. Even tate with different surface speeds. The roll I) is such repeated grinding and loosening of the masupported wholly Within the hopper a whilst the terial is not found to be adequate to ensure uniroll 0 forms part of one side wall of the hopper lil' formly fine grinding on the one hand and on the and the roll 9 forms the base of the hopper. The 10. other hand this method of treatment fails to sloping sides of the hopper walls together with liberate undesirable volatile constituents which the rolls b and 0 form the collecting chambers impart say, a disagreeable odour to the product. for the material which, although in the form of These second mentioned considerations apply in a paste or thick fluid must be considered as in cases such as the fine grinding of chocolate and the coarse state relatively to the fine state of 15 cocoa beans, so that in many such cases it is'necthe finished product. The coarse product is essary to pass the material through a separate shown at k. The first stage of the grinding takes stirring process which ventilates the material and place between the rolls 1 and c where the surenables the volatile constituents to pass off. face of one of the rolls moves at a greater speed The object of the present invention is to enthan the surface of the other so as to give a 20 able a very high degree of uniform fineness to be rubbing or grinding action. After leaving the obtained in the product from such grinding mills grinding point, the surfaces of both rolls are and also in connection with this grinding operacleaned by passing scrapers d and e which may, tion at the same time to free the material of unif desired be arranged so that their pressure on desirably smelling constituents all in a single pass the roll surface may be adjusted from outside. 25

through the machine. This action loosens the material from the roll sur- The invention consists of a grinding mill havfaces but does not break up the smaller cakes or ing a plurality of rolls forming a succession of clumps of material. The material 1 so loosened is grinding pairs through which the material is in a finer state of comminution than the material passed in series with collecting chambers for 1c in the hopper compartment in front of the 30 the material interposed between each grinding grinding pairb and 0. stage and which is characterized by the provision It will be understood that the side walls of the of stirring mechanism in the collecting chamber hopper a are arranged so close to the rolls 0 and 9 between any grinding pair and the next followthat none of the material can escape. ing pair in the series. The provision of the above described loosening 35 The effect of the interposition of this stirring means, that is scrapers d and e on the roller pairs mechanism is to subject the material which has 0 and b is known, but in accordance with this just left or been liberated from one grinding pair invention a stirring device 2' is provided in the to a mixing and breaking up operation which collecting chamber for the material 1 which has loosens the fine particles and liberates any undebeen loosened or scraped from the roll surfaces 40 sirable volatile constituents and at the same time by the scrapers d and e and this stirrer further this loosening has the effect of increasing the breaks up or loosens the powder or paste and grinding or comminuting action at the next folbrings it to a more uniformly thick liquid conlowing grinding pair. sistency free of lumps or cakes before the mate- The invention is illustrated in the .accompanyrial f passes to the grinding stage between the 45 ing drawing by way of illustration in a diagrampair of rolls 0 and g. matic fashion, it being evident that the details This active stirring operation thus ensures of the grinding and stirring mechanism form no that the small solid particles are relatively disimportant feature of this invention and may be placed and separated to open them up to the varied in a number of ways to suit different purmaximum grinding action at the next following 50 poses and materials under treatment. The diastage. If the material, as is frequently the case, gram shows a form of the invention in cross sechas been squeezed into the form of flakes or tion. scales these are brought by the stirrer into a In carrying the invention into effect according position throughout the mass which is in the to the form illustrated, a single hopper a is argreat majority of cases either at right angles or 55 at some inclined angle to the opening between t the rolls of the next following grinding pair,

whereas in former designs these flakes entered the second grinding pair more generally in a tangential path. In this way it is possible by means'of this invention to decrease the pressure between the second pair of grinding rolls and in position. The power consumption of the mill is thereby reduced.

What I claim is: 1. A grinding mill for use in grinding generally fiuid material possessingLundesirable vola+ tile constituents, said mill including three grind-r ing rolls cooperating to provide two grinding pairs between which all of the materialis passed in succession, an open chamber in constant communication with the atmosphere, said chamber being disposed in proximity to the discharge from the first grinding pair and being also disposed in proximity to the intake. of the second grinding pair, a generally stationary scraper operatively bearing against oneof the rolls constituting the first grinding pair and arranged to scrape material therefrom and into said open chamber, said scraper being transversely spaced from a wall of said open chamber to permit the undesirable volatile constituents of the material in said chamber to escape between said scraper and said chamber wall to the atmosphere, and a rotary stirrer separate from said scraper for agitating the material in said open chamber and for releasing said undesirable volatile constituents therefrom, said stirrer being disposed-within said 7 chamber, and transversely'spaced from the surfaces of the said rolls and the adjacent chamber walls, and rotatable about an axis generally parallel to the axes of said rolls, said stirrer having a surface movable into proximity to said grinding rolls to feed the material passed between the first grinding pair towards the bite of the second grinding pair. 7

' 2. A grinding mill for use in grinding generally fluid material possessing undesirable volatile constituents, said mill including three grinding rolls cooperating to provide two grinding pairs between which all of the material is passed in succession, the adjacent surfaces of the rolls constituting the first grinding pair travelling in the same direction, an open chamber in constant communication with the atmosphere, said chamber being disposed in proximity to the discharge from the first grinding pair, and being also disposed in proximity to the intake of the second grinding pair, and a rotary stirrer for agitating the material in said open chamber and for releasing said undesirable volatile constituents therefrom, said stirrer being disposed within said chamber and transversely spaced from the surfaces of the said rolls and the adjacent chamber walls, and rotatable about an axis generally parallel to the axes of said rolls, the direction of rotation of said stirrer beingopposite the direction of rotation of the first grinding roll, and said stirrer having a surface movable into proximity to said grinding rolls to feed the material passed between the first grinding pair towards the bite of the second grinding pair, whereby the material discharged from between the first grinding pair and entering said open chamber will be moved by said stirrer towards the bite of the second grinding pair along a path other than the shortest 

